1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, the present invention relates to a secondary battery including a safety vent having an adjustable fracture site thereof.
2. Description of the Related Art
Compact and light-weight portable electrical/electronic devices, such as cellular phones, notebook computers, camcorders and the like, are being actively developed and produced. Therefore, portable electrical/electronic devices have built-in battery packs so that the devices can operate even at locations where external power sources are unavailable. Recently, upon consideration of economical aspects, these battery packs employ secondary batteries that are capable of charging/discharging. Furthermore, secondary batteries are drawing attention in view of their use as batteries for hybrid automobiles, which require high energy density and high power output, and product development thereof is proceeding.
Representative examples of the secondary batteries include nickel-cadmium (Ni—Cd) batteries, nickel-hydrogen (Ni—MH) batteries, lithium (Li) batteries, lithium ion (Li-ion) batteries, and the like.
In particular, lithium ion batteries have an operating voltage approximately 3 times that of nickel-cadmium batteries or nickel-hydrogen batteries which are widely used in power supplies for portable electronic devices. Furthermore, lithium ion batteries are widely used from the viewpoint that the energy density per unit weight is high. Lithium ion batteries use a lithium-based oxide as a positive electrode active material, and use a carbon material as a negative electrode active material. In general, the batteries are classified, in accordance with the type of electrolyte, into liquid electrolyte batteries and polymeric electrolyte batteries. The batteries using liquid electrolyte are referred to as lithium ion batteries, while the batteries using polymeric electrolytes are referred to as lithium polymer batteries. The lithium ion batteries or lithium polymer batteries are put to use while accommodating the electrolyte in a metal case, a pouch type case, or the like, and the shape of the case may be exemplified by a cylindrical type, a square type, a pouch type or the like.
Secondary batteries, including lithium ion batteries and lithium polymer batteries, are sealed and have safety vents installed therein, which enable a portion of the case accommodating a secondary battery to be opened to release gas when the secondary battery is overheated due to overcharging, over-discharging, an internal short circuit and the like and is configured to release excess gas, so that an explosion of the secondary battery is prevented.
However, the structure of such safety vent makes it difficult to predict the shape of fracture thereof because the site of fracture thereof is not consistent when the safety vent is opened to prevent an explosion of the secondary battery. Thus, it is very difficult to design the structure of auxiliary joint structures, such as plastic covers and the joint positions.
Furthermore, there is also a problem in that the electrode assembly can be torn off, contacting the safety vent when an electrode assembly accommodated inside the case is inserted in a can.